1. Field of the Invention
The present invention relates to a planarizing process. More particularly, the present invention relates to a method of chemical-mechanical polishing in which a dummy pattern is used.
2. Description of the Related Art
Chemical-mechanical polishing is currently the only technique capable of providing global planarization in VLSI process, and even in ULSI process.
FIG. 1 is a schematic, top view diagram of a conventional wafer. FIGS. 2A and 2B are schematic, cross-sectional diagrams of FIG. 1 along a line II--II, which are used to depict steps in a chemical-mechanical polishing process.
Referring to FIGS. 1 and 2A, a die region 102 and a scribe line region 104 are defined on a wafer 100. A width of the scribe line is 110 .mu.m. A metal layer 106 is formed on the die region 102. A silicon dioxide layer 108 is formed to cover the wafer 100 and the metal layer 106 by chemical vapor deposition.
Referring to FIG. 2B, the silicon dioxide layer 108 is planarized by chemical-mechanical polishing.
As shown in FIGS. 2A and 2B, the height difference between the scribe line region 104 and the die region 102 is large because the metal layer 106 is formed on the die region 102 and nothing besides test keys is formed in the scribe line region 104, thus the surface of the silicon dioxide layer 108 is not formed flat. As a result, a part of the silicon dioxide layer 108 formed on the scribe line region 104 is easily polished in the chemical-mechanical polishing process, especially at an intersection between scribe lines. Therefore the uniformity of the silicon dioxide layer 108 is poor and a dishing effect occurs. Devices at a corner of the die region 102 are easily abraded.
FIGS. 3A and 3B are schematic, cross-sectional diagrams of FIG. 1 along a line II--II, which are used to depict steps in another chemical-mechanical polishing process.
Referring to FIG. 3A, a borophosphosilicate glass layer 110 is formed to cover the metal layer 106 and the wafer 100. A silicon dioxide layer 108 is formed on the borophosphosilicate glass layer 110.
Referring to FIG. 3B, the silicon dioxide layer 108 is planarized by chemical-mechanical polishing.
Although the borophosphosilicate glass layer 110 is formed to reduce the height difference between the die region 102 and the scribe line region 104, it has little effect. The dishing effect also occurs.